Yes. Commits clearly show in progress where both LGPL and MIT code was working together. This clearly show they are a derivative work and MUST follow the original license.
Plus the argument put forth is that they can re-license the project. It's not a new one made from scratch.
Did they eventually remove/replace all the LGPL code?
So, if these commits were private and squashed together before 7.0 was published there would be no violation?
The commits being public or not does not change the fact the developement was made as a derivative work of the original version.
They would be concealing the violation.
Consider TCC relicensing. They identified the files touched by contributors that wanted to keep the GPL license and reimplemented them. No team A/team B clean room approach used. The same happened here, but at a different scale. All files now have a new author and this author is free to change the license of his work.